The most common and most likely answer to this crossword clue is the 13 letter word DISCRETIONARY
I've seen this crossword clue in Financial Times
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More clues leading to the result DISCRETIONARY
Buddy explains!
The straight part
We know that "It’s as one decides" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it’s as one decides = discretionary.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does DISCRETIONARY mean?
DISCRETIONARY adjective- Available at one's discretion; able to be used as one chooses; left to or regulated by one's own discretion or judgment.